1. Field of the Invention
The present invention relates to an inverter module comprising a switching element group provided in a mold package to convert a DC voltage into a three-phase pseudo AC voltage by switching.
2. Description of the Related Art
Recently, an air conditioner equipped with an electrically driven compressor driven by a battery power source has been developed as an air conditioner for an electric automobile. This air conditioner comprises, as shown in FIG. 3, a battery (DC power source) 101, a switch 102 as a switching device connected in series to the battery 101, a charging device 111 connected in parallel to the switch 102 and including a resistor 104 and a switch 103, an inverter module 105, a condenser 106, and an electrically driven compressor 110.
The inverter module 105 is configured by molding, into a mold package 115, a switching element group 112 comprising a switching element 114 and an unshown diode to absorb a switching surge. This switching element group 112 converts a DC voltage from the battery 101 into a three-phase pseudo AC voltage, and applies it to the electrically driven compressor 110 to drive a motor of the electrically driven compressor 110.
Furthermore, the resistor 104 of the charging device 111 restricts an incoming current through the condenser 106 and an incoming current generated in the condenser 106 when the DC voltage of the battery 101 is applied. That is, the presence of the resistor 104 makes it possible to, when the battery 101 is connected, open the switch 102, close the switch 103, and pass a current via the resistor 104, thereby restricting the incoming current produced when the voltage of the battery 101 is applied. This can prevent a disadvantage where a high current or high voltage is applied to the inverter module 105 to damage the switching element group 112 and the like in the inverter module 105 (e.g., refer to Japanese Patent Publication Laid-open No. 3341327).
On the other hand, in such an air conditioner, the switch 102 might be welded to remain in a closed state despite a command being issued by an unshown controller to open the switch 102. Thus, heretofore, voltage dividing resistors have been provided before and after the switch 102, and terminal voltages of these voltage dividing resistors have been detected to check the occurrence of welding of the switch 102, but the provision of the voltage dividing resistors has posed a problem of increased installation space.